Schedule D is the old name for what we now call self assessment. If you have registered as self employed ie under CIS or working for yourself or have income that has not been taxed ie property letting, capital gains (selling a property) foreign income or trusts then you will need to complete a tax return. If it is just self employed income then you will need to provide your turnover figures and any receipted expenses you wish to claim for, which then will result in a profit or loss. If you believe that you should not be assessed under SA then call the tax office and ask why . If a tax return has been issued to you then by law you have to complete it and send it in otherwise you will get penalties.